Conventionally, when winding coils around core teeth, a high tension is applied to the coil wire which could cause the coating of the coil wire to be damaged by the edges of the core teeth. If there is any possibility of such an occurrence, the tension applied by the coil former (coil winding machine) to the coil wire must be reduced. Once the coils are fully wound around the core teeth, resin material is coated over the motor rotor.
A motor manufacturing process of this type typically comprises the steps of preheating the motor rotor, coating the resin material over the motor rotor, adjusting or trimming the coating, and curing the resin material. The coating step can be carried out by using an automated coating machine, but the trimming step has to be manually carried out, and the time period required from the start of the heating step to the completion of the curing step is so long (typically approximately two hours) that the coils which may have been initially fully received in the core slots may spring back out of the core slots by the time the curing step is completed.
Therefore, conventionally, as is illustrated in FIG. 4, as a counter measure to prevent coils 8, which are received in core slots 4a, from coming out of the core slots 4a, the bulging of the coils 8 in radially outward direction was restrained by placing a wedge 11 in each of the core slots 4a from an axial end of the core 4 so as to be engaged by the overhang portions of the adjacent core teeth 4a, after the coils 8 are wound around the core 4 of the motor rotor 3 and before the resin material is coated over the motor rotor.
However, as the number of core slots increases, the necessary number of wedges, as well as the amount of work involved, increases to such an extent that the cost of the component parts and the complication of the manufacturing process become substantial.